Styrene, also known, as vinyl benzene, is an aromatic compound that is produced in industrial quantities from ethylbenzene. The most common method of styrene production comprises the dehydrogenation of ethylbenzene, which produces a crude product of styrene and ethylbenzene. Polystyrene is an aromatic polymer produced from styrene monomer. Polystyrene is a widely used polymer found in insulation, packaging, and disposable cutlery, as well as foamed products including foam cups.
In preparing polystyrene, it may be desirable to initiate or increase the branching of polymer chains. Increased branching may impart physical property changes to the polymer including increased strength, higher temperature performance, and improved hardness. Additionally, increased branching may improve properties such as elastomeric performance and abrasion resistance.
Styrene monomer (SM) is often processed into many types of products, such as general purpose polystyrene (GPPS), high impact polystyrene (HIPS), transparent impact polystyrene (TIPS), and polystyrene foam. Many conditions affect the properties of the resulting product, including processing time, temperature, pressure, purity of the monomer feedstock, and the presence of additives or other compounds. These and other processing conditions alter the physical and chemical properties of the polystyrene product, affecting the suitability for a desired use.
Among the properties that must be controlled and balanced are averaged molecular weight (Mw) of the polymer, molecular weight distribution (MWD), melt flow index (MFI), the storage modulus (G′), the glass transition temperature (Tg), tensile strength, hardness, and toughness. Polystyrene typically reacts with hydrocarbon solvents and fats or oils, thus polystyrene may be blended or layered with another compound, or coated to limit this reactivity.
Melt strength is an important material property for thermoplastic processing. General-purpose polystyrene (GPPS), due to its generally linear molecular structure, has poor melt strength and demonstrates poor results in certain applications, such as in the production of films. Also, polystyrene foam is a useful form of polystyrene and polymer melt strength is an element for a foaming process. In the production of polystyrene foam, poor melt strength often leads to immature bubble breakage/coalescence, non-uniform cell morphology, and excessive open cell content. It would be desirable to obtain a polystyrene having a good melt strength in order to obtain polystyrene compositions that perform well in foaming processes and in the production of films.